Gas detection apparatus



May 28, 1946.

w. H. 4FAHR l-:TL I 2,400,923 GAS DETECTION APPAR-ATUS Filed llarjch 19, 1945 6 Horan/AUST GASES f 107 AIR,

NANJFoLp Patented May 28, 1946 GAS DETECTION APPARATUS Willard H. Farr and William F. Fagen, Chicago, Ill., assignors to Stewart-Warner Corporation, Chicago, Ill., a corporation o! Virginia I Application March 19, A1943, Serial No. 479,'l11

2 Claims. (Cl. ITF-311) The present invention relates to gas detection apparatus. Y Y l One of the objects of the present invention is to provide a new and improved apparatus of the type comprising a variable resistance heated lilament for detecting or indicating the presence of `a iluid.

Another object of the present invention is to provide new and improved detection apparatus of the type comprising a variable resistance heated lament, wherein means are provided for diffusing the ilow of uid past the lament so that the iiow and resulting resistance of Athe `iilament is substantially independent of the position of the nlament.

, Another and more specific object of the inven. tion is the provision of apparatus ofA the character set forth in the preceding paragraph, wherein the diffusing means is constituted by a `chemically inert material in the immediate vicinity of and surrounding the filament. In its preferred form the chemically inert material 4is constituted of loosely packed fibrous material, Y

such asglass wool. This material is light and does not change its position with changes in po sition of the filament. It minimizes the effect of convection currents and provides a moreuniiorm iio'w of iluid past the filament at all times, and also possesses low heat conductivity.

A further object of the present invention is to provide a. new and improved carbon monoxide indicating apparatus which is especially suited for the detection and indication of carbon monoxide in mobile equipment, such, for` instance, as an airplane.

The heat exchanger is indicated as a whole by reference character Il and it comprises a cold air intake I2. and a hot air duct I4 through which the heated air is supplied to the interior of the cabin. 'Ihe heater may be of the exhaust gas type or of the type wherein combustion takes placewithinthe heat exchanger. It is assumed, for the purpose oi-lllustration.that itis of the exhaust gas type. 'I'he hot exhaust gases iiow into the heat exchanger through a conduit I6 and are exhausted from the heat exchanger through a conduit ll.

It is important, in the event of leakage of exhaust gases into the heated air stream, that the presence of these gases, which include carbon monoxide, be detected and indicated so that steps may be taken, either manually or otherwise. to stop theleakage. Otherwise, the occupants of the cabin might very wellsuccumb to the effects of carbon monoxide poisoning. t

In the embodiment of the invention illustrated in Fig. 1 the presence of carbon monoxide is detected by a balanced circuitarrangement including a pair o f iilamentary resistance elements, preferably of the platinum wire type which are maintained at an elevated temperature so as to burn inflammable gases coming in contact therewith Unheated and heated air streams are Other objects and advantages of the present invention will become apparent from the ensuing description in the course of which reference is had to the accompanying drawing, in which Fig. 1 is a diagrammatic-representation of anv embodiment of the invention utilized for the purpose of detecting the presence of carbon mono'xide in the cabin of an airplane;

Fig. 2 is an enlarged fragmentary elevational view of one oi the two similar filaments and itsI associated housing utilized in the embodiment of the invention illustrated in Fig. 1; and

Fig. 3 is a cross sectional viewtaken along the line 'S-I o! Fig. 2. l

Referring to Figs. 1 to 3,1nc1us1ve, it may be passed in contact with the resistance elements so that; as long as the characteristics of the air flowing past the two filaments are the same, there is no unbalance of the circuit. However, should 4the heat exchanger become punctured, as'by a bullet, then the air flowing past one of the resistance elements becomes contaminated with carbon monoxide, hydrogenand water vapor, among other things, and the resistance of that element changes and unbalances the circuit.` The unbalance of the circuit is utilizedto operate an indicator.

The balanced circuit illustrated in Fig. 1 is of the Wheatstone bridge type and includes a pair of illaments 20 and 22, past which the unheated and heated air streams now. The resistors 2l and 26 are connected to the -illaments to form a sbridge.

stated generally that the illustrated apparatus is utilizedjto indicate the presence oi carbon monoxide in the cabin of an airplane. While the cabin has not been illustrated. the heat exchanger supplying heated air to the cabin has.

The bridge is preferably energized by a high ,frequency alternating current supplied to the bridge through conductors 28 and 30. The diagonals o i the bridge are connected by conductors 32 and 34 to a high gain amplifier 36, which may be of conventional construction; and the output of which is connected to a suitable indicator 38.

The unheated air nofws from the cold air intake Il'past and in contact with the illament 20,

through a line constituted by a conduit 40 connected to the intake, one section of a two-section heat exchanger s2, a conduit M connecting the heat exchanger to a housing or cell 46 having a chamber within which the filament is mounted and which embodiesone of the primary features of the present invention. The air flowing past the filament is exhausted through conduit 68.

In similar manner the heated air flows pastv unheated and heated air supplied to the cells 46 and 54 within which the filaments 20 and 22, respectively, are mounted. By equalizing the temperatures of the twoairy streams the teniperatures of the filaments will be similarly affected inso far as any temperature variations in the cold and heated air streams are'concerned.

As already indicated one of the important features of the present invention resides in diffusing the flow of fluid past and in contact with the filaments 20 and 22 in their respective cells. In brief, this desirable diffusing is achieved by surrounding each filament with a chemically inert material, such, for instance, as loosely packed fibrous glass wool.

Referring now more particularly to Figs. 2 and 3 it may be noted that the cell 54 comprises a metal container 60 provided with a relatively large analyzing chamber 62 substantially centrally of which the filament 22 is supported by a, pair. of upstanding spaced apart conducting posts 64. These posts are secured to `but, insulated from a bottom plate 65 detachably-securedy to the container 60.

izing chamber is Vdisposed parallel to the analyzing chamber andopens into the analyzing cavity through a longitudinal slot 10. A tubular piece of steel gauze is inserted into the equali'zing chamber and held in place therein by a removable se'rew 12. The air .thus admitted into the analyzing chamber flows out of the latter through a similar equalizing chamber 14 and communicating with the analyzing chamber by a 'longitudinal slot 15. l'I'his equalizing chamber is also closed by a, screw 16 and communicates 'with the l exhaust conduit 56.

Inasmuch as the cell 46 is similar to it is not deemed necessary to describe it.

In operation the cold air on the one hand and the heated air on the other are forced Vto ow through the-heat exchanger 42 where their temagudeza dicator 38 shows that there is no contamination of the heated air. In the event the heat exchangr develops a leak, then the air flowing past filament 22 is accompanied by water vapor, hydrogen and carbon monoxide, which change the temperature of the filament and its resistance to unbalance the bridge. This unbalance is amplifled by the amplifier 36 and shown by indicator 38.

One of the important advantages of the present invention resides in independence of the apparatus from the position of the filaments, Whereby-the apparatus may be advantageously used in equipment such as airplanes. The position of the airplane has no material effect on the resistance of the filaments, since the airflow past the filaments is diffused and rendered uniformby the glass wool. The effect of convection currents upon the indication of the presence of contaminating gases in the heated air stream is minimized.

Although the invention has been disclosed in conjunction with the specific details of a single embodiment, it should be understood that such details are not intended to be limitative of the invention except in so far as set forth in the accompanying claims.

Having thus described our invention what we claim as new and desire to secure by Letters Patent of the United States is:

l. In apparatus for detecting or indicating the presence of a fluid and of the type comprising a variable resistance heated filament mounted within a chamber, the combination including,

means supporting the filament in the chamber in the path of flow of fluids in the chamber, and a chemically inert loosely packedfibrous material in the chamber in the immediate vicinity of and surrounding the filament for diffusing the fluid flowing past the filament and for preventingconvection currents within the chamber.

2. In apparatus for detecting or indicating the presence of a. fluid and of the type comprising a variable resistance heated filament mounted within a chamber, the combination including, means supporting the filament in the chamber in the path of flow of fluids in the chamber, and 'loosely packed glass wool in the chamber in the immediate vicinity of and surrounding the filament for diusing the fluid flowing past the filament and -for preventing convection currents within the chamber.

WILLIAM F. FAGEN. 

